The present invention relates to an air-stream mill for free flowing materials, i.e., various ores and nonmetallic minerals, solid fuel, metallurgical compounds, inorganic products of calcination and baking, fertilizers and other chemicals, grain, bones and other materials of vegetable and animal origin.
The present invention can be utilized in power engineering, in mining, metallurgical, construction, chemical and food industries.
The mill according to the invention can be used for grinding materials practically to any size from a decimeter to micron dimensions.
An air-stream mill is known in the art comprising milling injectors facing each other; the material in these injectors is entrained by the gaseous working medium and accelerated to a speed which is near to that of the working medium, and a miling chamber with coaxially built-in injectors. The milling chamber provides for free collisons and crushing of the material being milled.
The known air-stream mill comprises a separator connected with the chamber milling for separating the finished product from the insufficiently ground material. The separator has spaces for separating the coarse and fine fractions of the half-finished product. These spaces are connected by the pipes which carry it for final grinding and are connected with the inlet pipes of the injectors.
The particles of the handled material in the known air-stream mills enter the counter-opposed injectors at atmospheric pressure and are accelerated there by the working medium (gas under pressure). They collide with each other at a high speed in the milling chamber. Thus the particles are disintegrated and discharged from the milling chamber through a central pipe into the separator.
The insufficiently ground particles of the material (half finished product) are separated in the separator from the finished product and return through the descending pipes into the milling injectors for repeated milling. The sufficiently milled material (finished product) is discharged from the separator being suspended in the working medium.
In the known air-stream mill large particles whose size is measured in centimeters cannot be milled since their pneumatic transportation from the milling chamber upward into the separator is limited by their weight.
In the base of the stream of the working medium located near the nozzle the gas density is very high so that introduction into it of the particles of the ground material falling by gravity into the injector is difficult (the material-entraining factor is low). Therefore, the specific consumption of the working medium for milling a unit weight of the material is relatively high.
To assure efficient separation in the separator of the finished finely-ground product from the coarse and fine fractions of the half-finished product all the particles of the material should be dispersed in a large volume of gas and be efficiently blown over by the latter. However, the amount of the working medium required for efficient milling is insufficient for such dispersion. Therefore, the air-stream mills usually utilize outside air drawn into the injectors or into the central pipe, said air being cheaper than the working medium but requiring for its movement along the entire mill duct and, often, for heating it to the ambient temperature, additional expenditures of the working medium and an increase in the power of the fan which discharges the used working medium from the mill.
The disadvantages quoted above limit the use of the air-stream mills for lump source materials whose crushing involves heavy material expenditures, in spite of the fact that these mills are efficient in some respects.